Mobs try to jump over an obstacle 1.5 blocks high

Video example of chicken following you
If you try to get a chicken to follow you and there's an obstacle 1.5 blocks high, the chicken will try to jump over it like it's 1 block high.
1) Get a chicken to follow you with a seed
2) Get behind an obstacle 1.5 blocks high
3) Chicken will try to jump over it (which is not intended)

Video of chickens trying to jump over 1.5 high blocks obstacle when trying to wander away
When a chicken tries to wander away it seems to ignore the slab on its way.
1) Get some chickens in a box with at least one wall 1.5 blocks high (it doesn't work when there are 5 or more snow layers on the block. Video example)
2) Wait until one of them tries to wander away or hit them so they'll try to run away
3) Some chickens (or the chicken you hit) will start jumping randomly

UPD: it works with any mob. Passive mobs, Hostile mobs
UPD2: mobs still try to jump over an obstacle even when there are more lower-half slabs above (screenshot 'ignoring lower half slabs')

From what I can see, this is a pathfinding algorythm problem